Clock circuits are used to synchronize or control the performance of various functions in electronic systems. These systems include but are not limited to mobile devices that perform wireless communications over a variety of channels. In a typical wireless device, display clocks, peripheral component clocks, memory clocks, and central processing unit (CPU) clocks can generate interference that diminishes the efficiency of platform wireless connections.
The main source of interference comes from harmonics of these clocks. These harmonics can overlap the frequency range of one or more wireless (radio) channels. This overlap may significantly reduce the data rate and/or operating range of the channel, thereby diminishing communication quality or limiting device capability.
Many such clocks use a technique called spread spectrum clocking (SSC) in order to reduce the energy levels of clock harmonics and comply with regulatory limits on electromagnetic emissions. However, this technique often increases interference with wireless receivers in the same system by spreading the harmonic energy into radio channels.